1. Field
One embodiment of the present invention relates to an optical disc drive, which moves a focus position of a light beam irradiated to an optical disc having a plurality of recording layers between these layers, and to a focus position control method.
2. Description of the Related Art
A digital versatile disc (DVD) and HD DVD have a plurality of recording layers. When information of other recording layer is reproduced from a certain recording layer, a light beam focus position is moved between layers, a so-called layer jump operation is made.
Jpn. Pat. Appln. KOKAI Publication No. 11-219530 discloses the following technique. According to the technique, amplitude information of a RF signal is monitored, and in a layer jump operation, a focus position diverges from a target position; for this reason, the amplitude of a RF signal becomes small. In this case, a hysteresis operation is carried out in order to forcedly restore the focus position to a target layer.
If a light beam passes through a damaged portion of an optical disc, the amplitude of a RF signal becomes small. Therefore, the hysteresis operation is made. As a result, servo becomes unstable; for this reason, there is a problem that time is taken until the layer jump operation is completed.